The objective of this proposal is to better understand how maternally derived antibodies can effect the developing humoral immune system. We have already characterized the neonatal HA-specific B-cell repertoire's early development, and determined how direct antigenic exposure can perturb this process. Since this background work is essential to any experiments aimed at understanding whether maternal factors affect the developing immune system, we are in a good position to begin such studies. In the proposed experiments, we will determine whether maternal antibodies enter the neonate's circulation structurally intact by treating nursing mothers with monoclonal (hybridoma) HA-specific antibodies, and following the fate of these antibodies in the mother and neonate. These studies will use radiolabeled antibody, antigen binding, and idiotype as measures of antibody transfer and integrity. HA-specific hybridomas of each major isotype will be used to determine whether different transfer properties exist. Further, we will determine the kinetics of transfer, by following the half life and decay properties of the transferred antibody. We will determine whether transferred maternal antibody influences the frequency of antigen-responsive B-cells in the neonate by limiting dilution analysis of HA-specific B-cells following the treatment of mothers with appropriate monoclonal antibodies. In addition, we will determine whether the frequency of specific regulatory T-cells changes due to maternally derived antibodies, and whether such antibody alters or prevents the induction of these regulatory circuits even when the neonate is challenged with antigen. We will assess TH cell frequency by limiting dilution, and TS cell activity with an in vivo assay for HA-specific suppression.